1. Field of the Invention
The present invention relates to radar systems. More specifically, the present invention relates to systems and methods for correcting for antenna gimbal biases.
2. Description of the Related Art
Guiding a missile to a target requires an accurate measurement of the target's three-dimensional location relative to the missile. Precise target location to the degree required for weapon midcourse/terminal engagement is well known for air targets but less so for ground targets where the engagement is typically based on radar seekers and imaging technology.
An imaging radar can determine the location of a ground target with the assistance of monopulse measurements that estimate the direction of each pixel in the radar image relative to the antenna boresight. An imaging radar system typically includes a radar antenna having a pointing mechanism, such as a gimbal or electronically scanned pointing, for controlling the direction in which the antenna is pointed. The pointing mechanism, however, may have unknown biases in its azimuth and elevation angles. These biases can lead to large errors in the apparent direction of the scene being imaged and, consequently, in the target location. Pointing biases vary from missile to missile and must be corrected for to ensure accurate measurements.
Factory alignment and on-aircraft target calibration can reduce gimbal biases, but these approaches are typically expensive and/or burdensome. Factory electrical alignment requires anechoic chambers that are expensive to build and maintain, since they themselves need calibration. Aircraft calibration targets also add to the cost of the aircraft, and raise maintenance costs. Neither of these options really simulates a target in the far field environment because of the limited space within which they are required to operate. Also, vibration from transportation or aircraft environments can introduce additional mechanical biases after the total initial biases, both electrical and mechanical, have been removed through calibration.
Hence, a need exists in the art for an improved system or method for correcting for antenna pointing biases that is less expensive and more accurate than prior approaches.